Denver, Colorado is called the "Mile High City" because its elevatoin is 5280 feet above sea level. Someone tells you that the elevation of Death Valley, California is -282 feet.
To find out how much higher Denver is that Death Valley, Frank provided the following solution:
Death Valley is 282 below sea level. Denver is 5280 feet above sea level. To find out how much higher Denver is than Death Valley, you will have to find the difference between the two elevations. So 5280-282 = 4998. Thus Denver, Colorado is 4998 feet higher than Death Valley, California.